Currently in 3GPP, under the name of LTE (Long Term Evolution), a wireless system adopting a new wireless technique has been studied. In this wireless system, a plurality of data channel resources are defined on a frequency axis to measure the state of quality of each channel and, based on the measurement results, a data channel resource for use in communication is determined. And, a notification about the data channel resource determined therein is made as allocation information by using a control channel to each terminal configuring the system mentioned above.
Also, in a downstream (base station→terminal) frame studied as LTE, a control channel and a data channel are disposed in one sub-frame, and resource allocation is performed in units of this sub-frame. Further, in a system frequency band, 100 channels are present according to current studies. And, each of these channels is called a resource block, and is configured of, for example, twelve sub-carriers. Still further, to each terminal configuring the system mentioned above, one or a plurality of resource blocks can be allocated.
Still further, in LTE, a terminal regularly measures channel quality in units of one resource block or several resource blocks, and reports the measurement result to a base station in which a scheduler is present. Then, based on the report, the scheduler allocates a resource block of good quality to a terminal that performs channel allocation. In this manner, in LTE, a technique of data transmission with resource-block allocation based on the channel quality is referred to as “Localized transmission”. In this Localized transmission, in notifying a terminal of allocation information, a bit map is used, for example. When a bit map is used, N resource blocks present in a system frequency band are associated with N bits, and a bit corresponding to a resource block to which a terminal is allocated is set at “1”. For example, when eight resource blocks are assumed, with a terminal A having allocated thereto resource blocks #0, #1, #6, and #7, a terminal B having allocated thereto resource blocks #2 and #3, and a terminal C having allocated thereto resource blocks #4 and #5, allocation information for notification by using control channels are “11000011”, “00110000”, and “00001100”.
However, as explained above, since 100 resource blocks are present at maximum in LTE, notification to each terminal by using a bit map of 100 bits leads to a shortage of control channels. To avoid this shortage, in 3GPP, a method of regarding two resource blocks as one scheduling unit (hereinafter referred to as aggregation) has also been studied. For example, when the number of aggregation is assumed to be 2 and the allocation information mentioned above is represented with a bit map, pieces of the allocation information for notification to the terminal A, B, and C are “1001”, “0100”, and “0010”, respectively. Note that while this method is in a studying stage in 3GPP, aggregation of three or four resource blocks has also been studied as a technique of reducing the control channels.
On the other hand, although the Localized transmission mentioned above is an effective technique when the traveling speed of the terminal is slow, it cannot be much an effective technique when the traveling speed is fast. For example, since reporting the channel quality and scheduling require a certain processing time, when the traveling speed is fast, changes of the channel quality in a direction of time is quickened, and therefore the contents of the report of the channel quality may possibly be obsolete at the time of actual data transmission. In such circumstances, since the possibility of allocating a resource block with deteriorated quality and the possibility of applying an unsuitable modulation technique or the like are increased, it is not preferable to select a resource block based on the channel quality of individual resource blocks and further adaptively change a modulation technique and an error correction coding rate. Therefore, to a terminal with a fast traveling speed, a technique is taken in which data to be transmitted by that terminal is distributed into a plurality of resource blocks with a small correlation each other as to the channel state on a frequency axis. That is, a technique is adopted such that an average value of the channel quality of the allocated resource blocks is stabilized (frequency diversity). And, when this technique is adopted, the modulation technique and the error correcting coding rate are determined not based on the channel quality of individual resource blocks but based on the average channel quality of the entire system frequency. In this manner, a technique of data transmission by allocating resource blocks distributed on the frequency axis to the same terminal is referred to as “Distributed transmission”.
While general outlines of Localized transmission and Distributed transmission have been explained above, a specific method of making a notification about the resource blocks allocated by the respective techniques is explained next. In a first non-patent document mentioned below, a method of making a notification about allocated resource blocks regarding the respective techniques is disclosed. FIG. 15-1 is a diagram depicting allocation information in this notifying method. In this example, by using a header bit, a notification is made about a distinction between Localized/Distributed transmissions (transmission type), a bit map size, and a resource block range corresponding to the bit map. And, FIG. 15-2 is a diagram for explaining how 34 bits at the time of Distributed transmission make a notification about resource in the method depicted in FIG. 15-1. For example, first thirteen bits indicate a start point: (0) for the allocated resource blocks and a resource block interval: (3), and next twelve bits indicate allocation in the resource block (x-th stage of a 12-way-split fragmented resource) as a bit map of the fragmented resource. Note herein that the remaining bits are assumed to be dummy bits for coordinating with the bit number at the time of Localized transmission.
Also, in a second non-patent document, “Sub-sampling transmission” is disclosed as a modification of the Localized transmission explained above. This Sub-sampling transmission is a method defined for allocating the remaining resources in units of one resource block after allocation of resource blocks with Localized transmission. Note that while the Localized transmission mentioned above and Sub-sampling transmission are both classified as Localized transmission and distinguished therein as approach 1 and approach 3, respectively, in 3GPP, they are distinguished hereinafter also as Localized transmission and Sub-sampling transmission for convenience.
FIG. 17 is a diagram for explaining Sub-sampling transmission. As depicted in FIG. 17, in Sub-sampling transmission, a concept of subsets is introduced, and their breaks are synchronized with the number of aggregation in Localized transmission. Specifically, when the number of aggregation in Localized transmission is M, the number of subsets is also M, and resource blocks configuring one subset are those obtained by periodically collecting certain M resource blocks aggregated in Localized transmission. And, the period is defined as [M resource blocks×M subsets]. In FIG. 17, an example of M=4 is depicted and, in this case, the period mentioned above is 4×4=16. Also, in this Sub-sampling transmission, resource blocks to be allocated to one terminal have to be selected from the same subset, and allocating resource blocks from different subsets to one terminal is not allowed.
First non-patent document: R1-072119 (May 7-11, 2007, RAN1 #49 Meeting, NEC)
Second non-patent document: R1-075067 (Nov. 5-9, 2007, RAN1 #51 Meeting, Ericsson)